Horacio Aguirre-Villegas

Life Cycle Impact Assessment and Allocation Methods Development for Cheese and Whey Processing

In this study, life cycle assessment (LCA) methods are used to develop life cycle inventory (LCI) and life cycle impact assessment (LCIA) data to estimate the global warming potential (GWP) and energy intensity (EI) of cheese and dry whey manufacturing in Wisconsin using a farm gate to plant gate approach. All of the environmental burdens and benefits are assigned to the product (cheese) and none are assigned to the land-spread waste stream (whey) for a single-output system typical of small cheese plants in Wisconsin. For a multifunction system, in which both cheese and food-grade whey are produced, the following methods are applied to handle co-product multifunctionality: subdivision, allocation ratios, and a method that combines both subdivision and allocation ratios. Total solids, nutritional content, and economic value are considered as the allocation ratios. Each of these fixed allocation ratios is applied to the entire process and to individual processes unique to each product. The differences in the GWP and EI for cheese and dry whey are highly influenced by the choice of method. The EI of cheese ranges from 7.1 to 19 MJ kg-1 cheese, and the GWP of cheese ranges from 0.46 to 1.3 kg CO2-eq kg-1 cheese. The main source of these differences is the shift of environmental burdens from cheese to the dry whey co-product resulting from different allocation strategies. The method that combines subdivision and allocation is presented as the preferred and most accurate method to deal with the multifunctionality of cheese and whey manufacturing. Sensitivity analysis shows that GWP and EI are most affected by variations in milk pasteurization, whey evaporation, whey drying, and whey pasteurization. This study demonstrates the importance of the allocation method on LCA analysis and suggests methods to more accurately assess the environmental burdens when more than one product is produced at a dairy plant.

Green cheese: Partial life cycle assessment of greenhouse gas emissions and energy intensity of integrated dairy production and bioenergy systems

The objective of this study was to evaluate the effect of integrating dairy and bioenergy systems on land use, net energy intensity (NEI), and greenhouse gas (GHG) emissions. A reference dairy farm system representative of Wisconsin was compared with a system that produces dairy and bioenergy products. This integrated system investigates the effects at the farm level when the cow diet and manure management practices are varied. The diets evaluated were supplemented with varying amounts of dry distillers grains with solubles and soybean meal and were balanced with different types of forages. The manure-management scenarios included manure land application, which is the most common manure disposal method in Wisconsin, and manure anaerobic digestion (AD) to produce biogas. A partial life cycle assessment from cradle to farm gate was conducted, where the system boundaries were expanded to include the production of biofuels in the analysis and the environmental burdens between milk and bioenergy products were partitioned by system expansion. Milk was considered the primary product and the functional unit, with ethanol, biodiesel, and biogas considered co-products. The production of the co-products was scaled according to milk production to meet the dietary requirements of each selected dairy ration. Results indicated that land use was 1.6 m2, NEI was 3.86 MJ, and GHG emissions were 1.02 kg of CO2-equivalents per kilogram of fat- and protein-corrected milk (FPCM) for the reference system. Within the integrated dairy and bioenergy system, diet scenarios that maximize dry distillers grains with solubles and implement AD had the largest reduction of GHG emissions and NEI, but the greatest increase in land use compared with the reference system. Average land use ranged from 1.68 to 2.01 m2/kg of FPCM; NEI ranged from -5.62 to -0.73 MJ/kg of FPCM; and GHG emissions ranged from 0.63 to 0.77 kg of CO2-equivalents/kg of FPCM. The AD contributed 65% of the NEI and 77% of the GHG emission reductions.

Grazing intensity affects the environmental impact of dairy systems

Dairy products are major components of the human diet but are also important contributors to global environmental impacts. This study evaluated greenhouse gas (GHG) emissions, net energy intensity (NEI), and land use of confined dairy systems with increasing levels of pasture in the diet. A Wisconsin farm was modeled to represent practices adopted by dairy operations in a humid continental climate typical in the Great Lakes region and other climates that have large differences in seasonal temperatures. Five grazing scenarios (all of which contained some portion of confinement) were modeled based on different concentrations of dry matter intake from pasture and feed supplementation from corn grain, corn silage, and soybean meal. Scenarios that incorporate grazing consisted of 5 mo of pasture feeding from May to September and 7 mo of confined feeding from October to April. Environmental impacts were compared within the 5 scenarios that incorporate grazing and across 2 entirely confined scenarios with and without on-farm electricity production through anaerobic digestion (AD). To conduct a fair comparison, all scenarios were evaluated based on the same total amount of milk produced per day where resource inputs were adjusted according to the characteristics of each scenario. A cradle-to-farm gate life cycle assessment evaluated the environmental burdens that were partitioned by allocation between milk and meat and by system expansion when biogas-based electricity was produced. Overall, results for all scenarios were comparable. Enteric methane was the greatest contributor to GHG emissions, and the production of crops was the most energy-intense process. For the confined scenario without AD, GHG emissions were 0.87 kg of CO2 equivalents, NEI was 1.59 MJ, and land use was 1.59 m2/kg of fat- and protein-corrected milk (FPCM). Anaerobic digestion significantly reduced emissions to 0.28 kg of CO2 equivalents/kg of FPCM and reduced NEI to -1.26 MJ/kg of FPCM, indicating a net energy producing system and highlighting the potential of AD to improve the sustainability of confined systems. For scenarios that combined confinement and grazing, GHG emissions ranged from 0.84 to 0.92 kg of CO2 equivalents, NEI ranged from 1.42 to 1.59 MJ, and land use ranged from 1.19 to 1.26 m2/kg of FPCM. All environmental impacts were minimized in scenarios that supplemented enough feed to increase milk yield but maintained dry matter intake from pasture at a level high enough to reduce material and energy use.

Global Warming Potential and Energy Intensity of Cheese Manufacturing in Wisconsin

Life Cycle Assessment (LCA) methods were used to quantify the Global Warming Potential (GWP) and Energy Intensity (EI) of cheese and dried whey manufacture in Wisconsin. Several allocation methods to assign environmental impacts to cheese and dried whey were compared: Economic, total solids, and nutritional value were each applied to the entire process and to individual processes unique to each product. The differences in the GWP and EI for cheese and dried whey were highly influenced by the choice of allocation method. The EI of cheese ranged from 5.08 MJ kg-1 to 15.01 MJ kg-1 and the GWP of cheese ranged from 0.31 kg CO2-eq kg-1 to 0.99 kg CO2-eq kg-1. This study demonstrates the importance of the allocation method on LCA analysis and suggests methods to more accurately assess the environmental burdens when more than one product is produced at a dairy plant.

Green Cheese: LCA of Energy Intensity and GHG Emissions of Integrated Dairy/Bio-fuels Systems in Wisconsin

The objective of this study was to estimate the effects of dairy diets, manure-handling methods, and interactions with the bio-fuels industry on the net energy intensity, greenhouse gas (GHG) emissions, and land use for milk production in Wisconsin. Five dairy diets supplemented with varying amounts of co-products from corn ethanol and soybean biodiesel production were modeled in two manure management scenarios: with and without on-farm biogas generation. The diets were characterized by different inclusion of soybean meal (SBM) and dry distillers grains with solubles (DDGS), balanced with different types forages. A partial life cycle assessment (LCA) of milk production from cradle to farm gate was performed. Milk production was used as the primary output for this analysis, since the dairy industry will remain the primary agricultural enterprise in Wisconsin for the foreseeable future. The boundaries of the milk production system were expanded to include bio-fuels production. The production of bio-fuels (corn ethanol and biodiesel) was scaled to meet the dietary requirements of each selected dairy ration. The choice of dairy ration had a substantial effect on GHG emissions and net energy intensity per energy corrected milk (ECM) produced. Land use for the integrated dairy and bio-fuels production systems ranged from 1.68 m2/kg ECM to 2.01 m2/kg ECM. Accounting for bio-fuels credits but without biogas generation, net energy intensity ranged from 0.83 MJ/kg ECM to 1.34 MJ/kg ECM, and GHG emissions ranged from 0.69 kg CO2-eq/kg ECM to 0.80 kg CO2-eq/kg ECM, depending on the diet. The average effects of including anaerobic digesters for on-farm biogas generation were reductions in GHG emissions by 0.24 kg CO2-eq/kg ECM, and in net energy intensity by 2.84 MJ/kg ECM.